Gripper... cooler weather is just around the corner.

Gripper,

I have one more theory for you.

I have been trying to figure out how a 10 to 20 degree difference in temperature could have such a big difference in MPG from what I am seeing (35 to 37 MPG in 80 to 95 degrees) vs. (27 to 34 MPG in 90 to 115 degrees)

I am starting to agree with you that there may be something in the charge control that is effecting your mileage, but it may be a safety feature, not a problem.

Apparently there is a sensor that monitors how hot the battery gets and reduces or shuts down the charge if necessary.

I have been searching the Internet trying to get confirmation about when this occurs, but it may be when the battery reaches 100 degrees or, more importantly, when the sensor thinks the battery is that hot.

If true, this might explain why both you and your Prius friends are getting such poor mileage when it appears all cars are functioning normally otherwise.

I hope this is right because as your temperatures cool down, you should see a big improvement and the solution would be some custom hack to keep the battery compartment under 90 degrees or so.

I will keep looking, as I'm very curious about this myself.

I had similar thoughts in my Camry Hybrid this winter, wondering if the fact that my trunk is so cold might be impacting battery performance. I started to test my theory by leaving the back seat down to allow the air to pass through into the trunk. Unfortunately, external issues kept me from getting any real data. I may try again this winter and I'll try to post back here. Of course, I have no idea if the NAH has any type of trunk pass-through, so this may not be very useful in this forum.

B. Goodman

A little piece of data? I went to the Lake on Sunday and we go over Mt. Ord at 4900 ft and it is coool there when you go down the other side the HV batter charge (voltagea0 indicator went clear up to the top pass the blue zone and to the very top. Indicating to me that it was really charging. I have never had this indicator go beyond about 80% in the blue region of the gage here in the valler Scottsdale where we live at 1490ft alt and 100f. I have the service manual and will try and locate the battery temp sensor and failing that will try and monitor the operation of the battery cooling fan and se if I could rout AC air to the inlet of the battery cooling fan or the temp sensor. There is a little accesss behind the center arm rest in the rear and could open it and leave it open and take a dryer vent duct and run it from the rear AC outlet to that little access door and see if it affects the operation of the battery charging. If so locating the sensor is a must and then doing the right thing to adjust it resistance change with temp to be just a bit mor favorable to efficient operation.

I have a fair bit of familiarity with this type of battery but not to anywhere the level Toyota has so I would not do anything drastic. Actually a small Peltier cooler and fan saw about a 50watt draw might be very good for cooling the battery champer in summer and reversing it in winter as i have read about pirus owners complaining about performance in winter beacuse tha battery is too cool being in the trunk.

O Lordy I wish I could just buy a duplicate Battery to hook in parallel with the current one and then add a plug. I am in the midle of a number of overwhelming personal problems that should soon be resolved and then I will have some time to get to work on this. Hope it's before the announcement of the a new battery/diesel/Plug/true-100mpg vehicle is announced that is afordable (actually it might be better if is was afterwards).

To add to this:

I have noticed here in the Bay area that when the outside temp goes over
90F (only 2-3 days so far this summer), the car goes into EV mode less
frequently.

Sometimes it will only go into EV mode only when speed is less than 30 mph instead of 40 mph even though battery has enough charge. The problem goes away after 10-15 mins of this type of behavior.

I think this is also due to the battery temperature sensor which frevents
rapid charge/discharge to stop the battery temperature from rising any
further. After some time battery cools down sufficiently (in 90F weather)
so that the normal behavior can resume.

igh,

My problem is finding information specific to the NAH on the Internet.

I have not even been able to prove this sensor exists on the Altima, only that folks think it exists on other hybrids.

I think GripperDon has the full technical manual and can look this up.

Incidentally I have had my NAH long enough to drive it in three days of 29-degree snow. I was able to get 35 MPG with the only loss coming from the full 10+ minute warm-up periods.

Gripper,

This is from the manual about battery cooling:

System Description

The HV ECU monitors rises in the battery temperature through the four temperature sensors in the HV battery module. Then, the hybrid vehicle control ECU steplessly actuates the cooling fan under duty cycle control, in order to maintain the temperature of the HV battery module within the specified range.

While the air conditioning system is operating to cool the cabin, if the HV battery module temperature is within a normal range, the hybrid vehicle control ECU turns the battery cooling fan OFF or changes the fan speed to low speed. The purpose of this control is to give priority to cooling down the cabin, which also provides cooling to the battery module through the intake duct located on the center of the rear package tray trim.

I recall that you were barely using your AC - set at a high temp and directed at your face - maybe that was causing some problems with the extreme heat in Scottsdale and the battery having to rely just on the fans as the AC was too minimal(?). Did you ever observe your fuel economy with the AC set to a more normal setting so the battery would get some of the cooling as well?

This is a fascinating thread.

I thought it was only me, but I thought "Gee, we aren't going into EV as much" as the summer months went on.

I will try it tomorrow, thanks for the great info!

Grip,


FWIW I own an 07 Camry Hybrid and also live in Scottsdale - McDowell Mtn. Ranch.

If I drive 'normally' I'll regularly average 36-38mpg per tank, but if I concentrate on keeping my pedal foot light, I can easily run 42mpg.

I keep my a/c at 65 degrees in ECO mode, and it's been on consistently since probably April.

Additionally, I am very familiar with Hwy 87 that you took towards Roosevelt Lake and Mt. Ord. The Mogollon Rim is one of my favorite places in the state, and within a month or so of getting my Camry last year, I had a run coming back from Pine, AZ (not Pinetop) where I averaged 56+mpg over 88 miles!! Granted, there's a lot of downhill from Pine to Scottsd, but also some pretty good hauls uphill - like that Mt. Ord section that got you a full charge.

Well, I guess my point here is to provide you some Camry #s logged in a climate exactly the same as what you're driving in.